Testing if recursion is TCOed

[inoas]

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So this is an inductive/brute force test (no proof).

Before I continue, because this is a bit tedious, I wanted to get a heads up if my approach is good and mergable in principle.

Obviously the TODO comments will be removed. I just went through some files and checked where I think recursion occurs, so that I can go through the test files and add a test case.

I started to omit should.-calls because the test case here is a non-crash. I have also added a comment to show why these strange test exists.

[lucasavila00]

It'd be interesting if the compiler was able to help with that. As is done in Kotlin with tailrec: https://stackoverflow.com/questions/51638557/what-is-the-point-of-tailrec-in-kotlin

If the function is not tail recursive the compiler flags it as an error.

[inoas]

@lpil is this the right way to proceed then I will go through the whole stdlib and add tests wherever I see (hope I don't miss) (tail) recursion.

[lpil]

Hello! Looks like a good approach to me! Though looks like a lot of work so may not be a good use of your time.

Thanks for waiting while I was on holiday for my reply

[inoas]

That's fine, I will get some more practise seeing (non)tcoed-recursion. I just don't want it be for nothing. I will work on this once I have some spare time. Thanks!

[inoas]

Unless I am mistaken for the list module, these functions need some improvements:

flatten, fold_right, unique, sort, transpose

[inoas]

For list.flatten() we could delegate these to:

• JS: Array.flat() see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/flat
• Erlang: List:flatten() see https://github.com/elixir-lang/elixir/blob/a64d42f5d3cb6c32752af9d3312897e8cd5bb7ec/lib/elixir/lib/list.ex#L206

[inoas]

list.sort() fails on JS only (node verison v16.15.0):

❌ gleam/list_test..sort_test: RangeError: Maximum call stack size exceeded

[inoas]

For list.unique on Beam the test runner times out on large numbers such as 999_999 different items, on the beam which makes sense because for 999_999 different items it needs to run 999_999 + 999_998 + 999_997 + .. + 1 AFAIU.

[inoas]

I have tried to port over https://github.com/lpil/gleeunit/pull/8/files#diff-2e01e4ff5ae575918bd323fb28192b743e863f3a0e22a408a43ca4ee7e0bd392 but if thrown error seems to be {}.

[inoas]

JS: list.sort and list.transpose are still not passing.

[inoas]

Thanks to @schurhammer list.sort is now passing the TCO tests. list.transpose has got a notice added to its docblock.

This is done from my side, so some review would be good to see if its ready to get merged.

[inoas]

Failing ci seems unrelated